Not The Limit Switch?


  #1  
Old 02-04-07, 03:15 PM
B
Member
Thread Starter
Join Date: Jun 2002
Location: Northern Minnesota
Posts: 1,628
Received 13 Upvotes on 9 Posts
Not The Limit Switch?

I have a Coleman 7900 Series natural gas furnace.

Mobile home.....installed new in 1988

I've noticed the last couple years after the furnace has run a few minutes the burner will shut off for a minute or two then comes back on till the thermostat shuts it down. This usually happens in the morning when you crank it up 5 degrees or so or when the filter is dirty.

I figured it was the limit switch shutting it down. Read on the furnace today it has a MANUAL limit switch, you reset it by pressing the red button. I've never had to reset it manually.

Is it possible it is resetting itself? Only thing I can think of.

Little cool last night, minus 27 and expecting minus 32 tonight, I'm just taking the top half of the door right off so it gets lots of air, doesn't seem to shut down then.

I have all the registers wide open except the one under my bed, hate waking up with my feet on fire.

Any ideas?

Thanks

Baldwin
 

Last edited by Baldwin; 02-04-07 at 03:38 PM.
  #2  
Old 02-04-07, 04:13 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Two limits

If I am not mistaken, that furnace has two limits. One is the manual reset & is visible. The other is an automatic reset & is behind a rectangular sheet metal box about 3x6".
 
  #3  
Old 02-04-07, 05:43 PM
B
Member
Thread Starter
Join Date: Jun 2002
Location: Northern Minnesota
Posts: 1,628
Received 13 Upvotes on 9 Posts
Grady, you hit that one on the nose. Thanks. I took the cover off the small box but for whatever reason not the big one.

http://i25.photobucket.com/albums/c98/Oriley/Furnace1.jpg


Like I said, it seems to be happening more often than before. Do these limit switches weaken over time?

Only reason I ask is I'd hate to call the gas company out at 3 AM when it's 30 below when I could do on a business day.

Thanks again,

Baldwin
 
  #4  
Old 02-04-07, 07:16 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Limit

Yes they do get weak. Might not be a bad idea to pick up a spare fan switch also. I think the fan is the one with the black wires & the limit is wired with red. I could be backward on that. Make sure you get the ones used in a Coleman as they are deeper than ordinary Thermo-disc switches.
 
  #5  
Old 11-20-11, 02:09 PM
B
Member
Thread Starter
Join Date: Jun 2002
Location: Northern Minnesota
Posts: 1,628
Received 13 Upvotes on 9 Posts
Grady, rather than private messages I'll put the rest of the mystery here.

1988 Coleman natural gas furnace

Model: 7975A856 Serial: 078868304


Here's the label on the limit switch, hard to read:




And a couple more of the limit switch:










Seems odd I can find the fan switch with no problem but not the limit switch.

Thanks
 
  #6  
Old 11-20-11, 02:16 PM
B
Member
Thread Starter
Join Date: Jun 2002
Location: Northern Minnesota
Posts: 1,628
Received 13 Upvotes on 9 Posts
I can find a limit 150-20 in size 60T11 but mine sure likes like a 60T13 to me which I can't find. Anyone know what the difference would be?

Thanks
 
  #7  
Old 11-22-11, 07:50 AM
B
Member
Thread Starter
Join Date: Jun 2002
Location: Northern Minnesota
Posts: 1,628
Received 13 Upvotes on 9 Posts



A) two black wires crimped together

B) one gray wire from transformer

C) nothing hooked to this


Seeing nothing goes to the third terminal (C) couldn't I just buy a regular 2 terminal limit like this one:




I don't know, but if the temp is correct and it fits in the hole I see no problem. Or is there???


 
  #8  
Old 11-22-11, 03:31 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
That limit has been replaced before. The one you have pictured certainly should be fine.
 
  #9  
Old 11-22-11, 04:46 PM
B
Member
Thread Starter
Join Date: Jun 2002
Location: Northern Minnesota
Posts: 1,628
Received 13 Upvotes on 9 Posts
I kind of figured that but wasn't sure. I'll order one tonight.

Thanks very much!
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: